Porous Coated Member and Manufacturing Method Thereof Using Cold Spray

ABSTRACT

Disclosed is a coated member on which a porous metal coating layer is formed and a method of producing the same. The method comprises providing the mother material, feeding powder having a metal composition, which includes at least two different metals selected from the group consisting of Al, Mg, Zn, and Sn and which is expressed by xA-(1−x)B (0&lt;x&lt;1, where x is a weight ratio of A and B), onto the mother material, supplying high pressure gas to the powder, applying the metal powder using on the mother material by spraying the metal powder using the high pressure gas through an supersonic nozzle, and heat-treating the coated mother material to form the porous coating layer. In the method, it is possible to freely control the pore size and porosity of the coated member. Accordingly, it is available to various members for thermal and mechanical applications.

TECHNICAL FIELD

The present invention relates, in general, to a coated member on which aporous coating layer is formed and a method of producing the same and,more particularly, to a method of forming a porous coating layer on asurface of mother material using a low temperature spraying process anda coated member in which a pore distribution and a size of the coatinglayer are controlled.

BACKGROUND ART

Formed on a surface of a member, a porous coating layer improves thermaland mechanical properties of the member.

For example, if a porous coating layer which includes open porescommunicating with each other is formed on the surface of a heatexchanger, the heat exchanger has an increased area of contact withsurrounding air, thereby assuring efficient heat exchanging performance.Meanwhile, sometimes, it is expected for a friction member to have lowstrength and hardness depending on its relationship with surroundingcomponents. The porous coating layer can satisfy this requirement.Furthermore, when mother material is joined with a different kind ofmaterial, stress may occur due to lattice misalignment at an interface.The porous coating layer can act as a buffer layer for avoiding stressduring the joining.

Conventionally, various coating methods have been employed as a methodof forming a metal coating layer on the surface of a member for thermaland mechanical applications. With respect to this, the method may beexemplified by an electroplating process, a hot dip plating process, orthermal spraying process. However, these processes have limits in termsof application, or may cause thermal impact to the mother material orthermal deformation of the mother material. Additionally, in practice,it is difficult to artificially control the porosity and poredistribution of the coating layer using the above processes.

As well, the thermal conductive metal coating layer which is applied topipes of the conventional heat exchanger corrodes or is mossy on asurface thereof in a corrosive environment, such as waste water or seawater, thus it does not perform its function. Accordingly, it isproblematic in that durability is not assured.

DETAILED DESCRIPTION OF INVENTION

An object of the present invention is to provide a member for thermaland mechanical applications, which does not cause thermal deformation ofmother material or damage to the mother material due to thermal impactand which is capable of being applied to various fields, and a method offorming a porous coating layer used in the member.

Another object of the present invention is to provide a member forthermal and mechanical applications, in which porosity, a pore size, anda pore distribution of a surface coating layer are capable of beingcontrolled, a method of forming a porous coating layer used in themember, and a porous coated member produced using the method.

A further object of the present invention is to provide a method offorming a porous coating layer having high thermal conductivity, whichis capable of being used in an external corrosive environment for a longtime.

In order to accomplish the above objects, the present invention providesa method of forming a porous coating layer on mother material. Themethod comprises providing the mother material, feeding powder having ametal composition, which includes at least two different metals selectedfrom the group consisting of Al, Mg, Zn, and Sn and which is expressedby xA-(1−x)B (0<x<1, x is a weight ratio of A and B), onto the mothermaterial, supplying high pressure gas to the powder, applying the metalpowder on the mother material by spraying the metal powder using thehigh pressure gas through an supersonic nozzle, and heat-treating thecoated mother material to form the porous coating layer.

According to an embodiment of the present invention, in the method asdescribed above, A is Al, and B includes a metal element selected fromthe group consisting of Mg, Zn, and Sn. Furthermore, it is preferablethat the heat-treatment of the coated mother material be conducted at atemperature between a eutectic temperature of A and B and a meltingpoint of a metal having the higher melting point of A and B. In detail,the heat-treatment is conducted at about 200-650° C.

Additionally, the feeding of the powder may further comprise changing xto change the composition of the powder.

As well, the present invention provides a metal coated member. The metalcoated member comprises metal mother material, and a coating layerformed on the metal mother material, which includes at least two metalelements and is expressed by xA-(1−x)B (x is a weight ratio of A and B).A and B are different metals selected from the group consisting of Al,Mg, Zn, and Sn, x changes when moving in a thickness direction of thecoating layer within a range of 0<x<1, and porosity of the coating layeris changed depending on a change in x.

According to the embodiment of the present invention, in the abovemember, x increases or decreases moving in a thickness direction of thecoating layer, and the porosity of the coating layer is increased ordecreased as x is increased or decreased. Additionally, A is Al, B isany one metal selected from the group consisting of Mg, Zn, and Sn, andx is decreased and the porosity of the coating layer is increased movingfrom an interface of the metal mother material and the coating layer toa surface of the coating layer.

As well, the present invention provides a metal coated member. The metalcoated member comprises metal mother material, and a coating layerformed on the metal mother material, which includes at least two metalelements and is expressed by A-B. A and B are different metals selectedfrom the group consisting of Al, Mg, Zn, and Sn, A or B selected fromthe above group changes when moving in a thickness direction of thecoating layer, and porosity of the coating layer is changed depending ona change in A or B.

In the present invention, the coating layer may include open pores whichare at least partially interconnected with each other, and it ispreferable that the open pores exist in an upper part of the coatinglayer in specific application fields.

Additionally, the present invention provides a method of forming aporous carbon coating layer on mother material. The method comprisesproviding the mother material, feeding carbon powder which isconglomerated by an organic binder, supplying high pressure gas to thecarbon powder, and applying the carbon powder on the mother material byspraying the carbon powder using the high pressure gas through asupersonic nozzle.

In the above method, the organic binder which is used to make the carbonpowder coarse may be at least one selected from the group consisting ofpolyvinyl alcohol (PVA), rosin, resin, polyvinyl butyral (PVB), andpolyethylene glycol (PEG). It is preferable that the organic binder becontained in a content of 10-30 wt % based on carbon.

Furthermore, in the above method, the coating layer may be additionallysubjected to a step of burning out the organic binder at 400-500° C.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 schematically illustrates a low temperature spraying system 100used to form a coating layer in the present invention;

FIGS. 2 a and 2 b are flow charts showing the formation of the porouscoating layer, according to an embodiment of the present invention;

FIG. 3 is a sectional view of a coated member 200 which includes acoating layer having a variable composition, according to the embodimentof the present invention;

FIG. 4 is an optical microscope picture of a section of a coating layerhaving a composition of 0.5Al-0.5AlMg after heat treatment, according tothe embodiment of the present invention;

FIG. 5 is an optical microscope picture of a section of a coating layerhaving a composition of 0.3Al-0.7AlMg after heat treatment, according tothe embodiment of the present invention;

FIG. 6 is an optical microscope picture of a section of a coating layerin which Al/AlMg/Al/AlMg/Al components are sequentially layered afterheat treatment, according to the embodiment of the present invention;

FIG. 7 is an optical microscope picture of a section of a coating layerin which 0.667Al-0.333Mg/0.5A1-0.5Mg components are sequentially layeredafter heat treatment, according to the embodiment of the presentinvention;

FIG. 8 is an optical microscope picture of a section of a coating layerhaving a composition of 0.5Al-0.5Sn after heat treatment, according tothe embodiment of the present invention;

FIG. 9 is an optical microscope picture of a section of a coating layerin which 0.667Al-0.333Sn/0.5Al-0.5Sn components are sequentially layeredafter heat treatment, according to the embodiment of the presentinvention;

FIG. 10 is an optical microscope picture of a section of a coating layerin which 0.667Al-0.333Zn/0.5A1-0.5Zn components are sequentially layeredafter heat treatment, according to the embodiment of the presentinvention;

FIG. 11 is a flow chart showing the formation of a porous carbon coatinglayer, according to another embodiment of the present invention; and

FIGS. 12 a and 12 b are electron microscope pictures of a section and asurface of the carbon coating layer formed through the procedure of FIG.11.

BEST MODE

Hereinafter, a detailed description will be given of the presentinvention, referring to the drawings.

FIG. 1 schematically illustrates a low temperature spraying device 100which accelerates powder to form a coating layer on a substrate (S) inthe present invention.

The spraying device 100 accelerates the powder for forming the coatinglayer at subsonic or supersonic speed to apply it to the substrate (S).With respect to this, the spraying device 100 comprises a gas compressor110, a gas heater 120, a powder feeder 130, and a spraying nozzle 140.

The powder of about 1-50 μm fed from the powder feeder 130 is sprayedusing compressed gas of about 5-20 atm supplied from the gas compressor110 through the spraying nozzle 140 at a rate of about 300-1200 mm/s.The powder sprayed in conjunction with the gas collides with thesubstrate (S). In this regard, kinetic energy of the powder plasticallydeforms the powder when the powder collides against the substrate (S),and provides bonding strength to the substrate, thereby forming thecoating layer having very high density.

In the device 100, the gas heater 120 which is positioned in a path forfeeding the compressed gas is a supplementary unit for heating thecompressed gas to increase the kinetic energy of the compressed gas soas to increase the spraying speed of the spraying nozzle. Furthermore,as shown in the drawing, a portion of the compressed gas may be fed fromthe gas compressor 110 into the powder feeder 130 so as to nicely feedthe powder into the spraying nozzle 140.

The compressed gas for the device 100 may be exemplified by somecommercial gases, such as helium, nitrogen, argon, or air, and the kindof gas used may be appropriately selected in consideration of thespraying speed of the spraying nozzle 140 and economic efficiency.

The operation and structure of the device are disclosed in detail inU.S. Pat. No. 5,305,414 by Anatoly P. Alkimov et al., and a descriptionof them is omitted herein.

FIG. 2 a is a flow chart showing the formation of the coating layer onthe mother material or the substrate using the spraying device describedreferring to FIG. 1.

With reference to FIG. 2 a, the method of the present invention startsfrom the step (S210) of feeding metal powder containing two or moremetals from the powder feeder 130 of the spraying device 100 and thestep (S220) of feeding compressed gas at high pressure from the gascompressor 110.

In the step (S210) of feeding the powder, the powder containing two ormore metals includes a mixture or a solid solution of at least twometals selected from the group consisting of Al, Mg, Zn, and Sn, or amixture of both. Furthermore, the metals selected in the presentinvention are different from each other. For example, if one metalselected from the above group includes Al, a composition of the metalpowder may be a binary system, such as Al—Mg, Al—Zn, or Al—Sn, a ternarysystem, such as Al—Mg—Zn, or a system having more than three metals.Additionally, in addition to the enumerated metals, Ti, Si, Mn, Cr, Fe,Co, Ni, or Cu may be also used without departing from the spirit of thepresent invention.

In the present invention, the powder having the metal components may beprovided in the form of solid solution. For example, the metal powdercontaining Al—Mg may be provided in the form of AlMg solid solutionwhich is so-called Magal. In addition, the powder having the metalcomponents may be provided in a mixture of the solid solution powder andthe monolith powder. For example, the metal powder may be a mixture ofAl powder and AlMg powder. Since the metal powder containing Mg isdangerous to handle, for example, it may cause explosions, it isprovided as a solid solution to assure ease of handling.

When the coating layer of the present invention is used in membershaving thermal and mechanical applications, since the metal powder hasrelatively good thermal and mechanical properties, such as thermalconductivity or strength, compared to its specific gravity, it ispreferable that it contain Al or an Al alloy extensively used in machinemembers.

In the step (S220) of feeding the compressed gas of the presentinvention, the gas may be exemplified by helium, nitrogen, argon, or airas described above. The gas is compressed by the gas compressor topressure of about 5-20 atm and is then provided. If necessary, thecompressed gas may be provided while being heated to about 200-500° C.using a heating unit, such as the gas heater 120 of FIG. 1. However,even though the compressed gas is heated according to the embodiment,the temperature change of the metal powder is insignificant due to thevery low specific gravity of the gas. Accordingly, the spraying step ofthe present invention is different from a conventional spraying process,in which the powder is heated and coated at a melting point or higher,in that the spraying is conducted at low temperatures.

Meanwhile, as described above, a portion of the compressed gas used inthe step (S220) of feeding the compressed gas may be used as carrier gasfor continuously and stably feeding the metal powder.

Next, a mixture of the compressed gas and the metal powder is sprayedusing the supersonic spraying nozzle (S230). The flow rate of thegas-powder mixture sprayed through the nozzle depends on the temperatureand pressure of the gas and the particle size and specific gravity ofthe powder. The gas-powder mixture having the particle size of about1-50 μm is sprayed at the rate of about 300-1200 m/s under the pressureand temperature conditions of the fed gas.

The metal powder which is sprayed at the high rate collides against themother material to form the high density coating layer. The sprayingstep (S230) is conducted until the coating layer having a desiredthickness is formed, and the coating layer thus formed is then heattreated (S240). In the present invention, it is preferable that the heattreatment temperature be about 200-650° C. The heat treatmenttemperature of 650° C. or higher causes complete melting of the metalcoat, and the coat is barely melted at the temperature of 200° C. orlower, resulting in a negligible heat treatment effect.

The high density coating layer formed on the mother material issubjected to the heat treatment step (S240) to acquire porosity. Aswell, as seen in the embodiment described later, porosity and the poresize of the porous coating layer depend on the change in composition ofthe applied metal powder. In this regard, the “change in composition” asused herein is intended to include a change in quantity as well asmetals used.

FIG. 2 b shows the method of forming the porous coating layer, whichcomprises the step (S250) of changing the composition of the metalpowder so as to control a pore distribution of the coating layer, withrespect to the coating method of the present invention describedreferring to FIG. 2 a.

According to the method, the composition of the powder is changed in thecourse of forming the coating layer during the step of spraying usingthe nozzle (S240). For example, after the powder having the compositionof 0.5Al-0.5Mg, in which a weight ratio of Al:Mg is 1:1, is fed for apredetermined time, the ratio is controlled to 1:2, or the powder havingAl—Zn instead of Al—Mg, in which a ratio of Al:Zn is 1:1, is fed,thereby forming the coating layer which has a vertical compositiongradient or contains different components.

The change in composition of the powder may be achieved through atypical procedure well known to those skilled in the art. For example,powders having different compositions may be sequentially fed into onepowder feeder, or, after a plurality of powder feeders for storing thepowders having the different compositions are prepared, the powderfeeder containing the powder having the desired composition may beselected using valves.

FIG. 3 is a sectional view of a coated member 200 which includes thecoating layer formed through the procedure.

With reference to FIG. 3, an Al—Zn layer 210 having a weight ratio of2:1, an Al—Zn layer 220 having a weight ratio of 1:1, and an Al—Zn layer230 having a weight ratio of 1:2 are formed on the mother material (S),such as Al. According to the embodiment of the present invention asdescribed later, if the coating layer is heat treated, the Zn contentincreases, thus increasing the pore size and porosity. Hence, if themember which is coated with the powder having the composition shown inFIG. 3 is heat treated, it is possible to form the coated member inwhich porosity and/or a pore volume increase moving away from the mothermaterial. The pore distribution as described above is desirable becauseit contributes to the stable coating at an interface between the coatinglayer and the mother material. Furthermore, in the structure as describeabove, since porosity and the pore volume increase, the pores formed atan outermost surface of the coating layer may be open porescommunicating with each other. Particularly, the open pores play animportant role in improving a heat exchanging property of the mothermaterial.

As described above, the change in pore distribution of the coatinglayer, which is described referring to FIG. 3, may be obtained bychanging the quantities of the components or by changing the types ofcomponents. In other words, it is possible to produce a coated member,in which porosity and/or the pore size increase moving away from theinterface, by sequentially layering Al—Mg, Al—Zn, and Al—Sn layers onthe mother material.

FIG. 11 is a flow chart showing the formation of a porous carbon coatinglayer, according to another embodiment of the present invention.

With reference to FIG. 11, first, carbon powder having an averageparticle size of 10 μm or less is mixed with at least one binderselected from the group consisting of PVA, PVB, PEG, resin, and rosin(S310). The mixing is conducted using a suitable solvent, that is, anorganic solvent, such as water or alcohol, depending on the type ofbinder.

Subsequently, the resultant slurry is dried to produce a carbon powdercake, and the cake is pulverized and sorted, thereby producing carbonpowder having a particle size that is suitable to the nozzle spraying,for example, an average particle size of 50-200 μm (S320 to S340).Thereafter, the carbon powder is conglomerated using the organic binderto be made coarse in comparison with the original size of the powder.

Next, the resulting carbon powder is sprayed in conjunction with highpressure gas of about 4-7 kgf/cm² (S350) using a low temperaturespraying device described referring to FIG. 1 through the nozzle so asto form the coating layer on the mother material (S350). In addition, aburn out process may be conducted at about 400-500° C. to remove theorganic binder from the coating layer.

A better understanding of the present invention may be obtained throughthe following preferred examples.

Physical properties of metals used in the following examples 1 to 7 aredescribed in Table 1. TABLE 1 Metal Melting point (° C.) Density (g/cm²)Al 660.2 2.699 Mg 650 1.74 Zn 419.46 7.133 Sn 231.9 7.298

Spraying conditions of a nozzle in examples 1 to 7 are as follows.Nozzle: standard laval type aperture: 4 × 6 mm throat gap: 1 mmCompressed gas: type: air pressure: 7 atm temperature: 330° C. Size ofpowder fed: <44 μm (325 mesh)

EXAMPLE 1

Mixture powder which includes Al powder and AlMg powder (eutectictemperature of about 400° C.) in a weight ratio of 50:50 (i.e.0.5Al-0.5AlMg) and air at 7 atm were fed into a spraying nozzle to beapplied on an aluminum substrate.

The resulting coating was heat treated at about 620° C. for 1 hour. Theheat treated substrate was cut and polished, and cross section wasobserved using an optical microscope. FIG. 4 illustrates a picture ofthe cut surface of the resultant substrate.

From FIG. 4, it can be seen that the coating layer is nicely attached tothe Al substrate. An interface between the Al substrate and the coatinglayer is apparent due to pores (black portions) trapped in the coatinglayer. The pores were not observed during the coating, but weregenerated after the heat treatment.

EXAMPLE 2

A coating layer was produced under the same conditions as example 1except that the weight of AlMg increased in the mixture powder so thatthe metal powder had a composition of 0.3Al-0.7AlMg. The coating layerwas heat treated, a section was observed using an optical microscope,and the results are shown in FIG. 5.

In comparison with FIG. 4, from FIG. 5, it can be seen that the size ofthe pore is increased, and an increase in porosity can be confirmed evenwith the naked eye.

EXAMPLE 3

A coating layer was formed in such a way that Al powder/AlMg powder/Alpowder/AlMg powder/Al powder were sequentially layered. The remainingcoating conditions were the same as example 1. Subsequently, theresulting coating layer was heat treated at 620° C. for 1 hour.

FIG. 6 is an optical microscope picture showing a section of a heattreated substrate. As shown in the drawing, pores were scarcely observedin the Al layer, but frequently observed in the AlMg layer.

EXAMPLE 4

An Al substrate was coated with mixture powder having a composition of0.667Al-0.333Mg, and then with another mixture powder having acomposition of 0.5Al-0.5Mg. The remaining coating conditions were thesame as example 1. Subsequently, the resulting coating layer was heattreated at about 620° C. for 1 hour, and a section was observed using anoptical microscope.

FIG. 7 is an optical microscope picture of the section. From FIG. 7, itcan be seen that the porosity of a coating portion (an outermostsurface) having the composition of 0.5Al-0.5Mg is higher than that of acoating portion (an interface) having the composition of0.667Al-0.333Mg. Accordingly, it can be seen that the porosity of thecoating layer increases as the Mg content increases. Additionally, fromthe shape of the pores and the porosity, it may be presumed that thepores at the outermost surface are open pores communicating with eachother. As described above, the pores, which are interconnected with eachother and are distributed from the outermost surface of the coatinglayer to the inside thereof, increase the area of contact withsurrounding air. Thus, particularly, it is available to applicationsrequiring excellent heat exchanging or heat radiation properties.

EXAMPLE 5

An Al substrate was coated with mixture powder of Al and Sn, which had acomposition of 0.5Al-0.5Sn. The remaining coating conditions were thesame as in example 1.

The resulting coating layer was heat treated at about 650° C. for 1hour, and a section was observed using an optical microscope after itwas polished. FIG. 8 is an optical microscope picture of the section. Asshown in FIG. 7, very many pores were observed in the coating layer.Judging from the shape of the pores and the porosity, the pores seem tobe interconnected with each other.

EXAMPLE 6

Mixture powder having a composition of 0.667Al-0.333Sn was appliedthrough the same procedure as in example 1, and another mixture powderhaving a composition of 0.5Al-0.5Sn was subsequently applied. Theresulting coating layer was heat treated at 620° C. for 1 hour, and apolished section was observed using an optical microscope.

FIG. 9 is a picture of the section. From comparison of an interfaceportion coated with 0.667Al-0.333Sn with an outermost surface portioncoated with 0.5Al-0.5Sn, it can be seen that the pore size issignificantly higher and porosity is higher at the outermost surfaceportion. Accordingly, it can be seen that an increase in the Sn contentpromotes the generation of pores.

EXAMPLE 7

An Al substrate was coated with mixture powder having a composition of0.667Al-0.333Zn, and then with another mixture powder having acomposition of 0.5Al-0.5Zn. The coating conditions were the same asexample 1. Subsequently, the resulting coating layer was heat treated atabout 620° C. for 1 hour, a section was observed using an opticalmicroscope, and the results are shown in FIG. 10.

From FIG. 10, it can be seen that many pores are formed in the coatinglayer due to the addition of Zn. Additionally, it can be seen that verylarge pores exist and porosity is higher at an outermost surface portionhaving a high Zn content in comparison with an interface portion havinga relatively low Zn content. Therefore, it can be seen that the poresize and porosity increase as the Zn content increases.

From examples 1 to 7, it can be seen that Mg, Zn, and Sn which are addedto the coating layer in conjunction with Al contribute to the formationof pores in the coating layer after heat treatment. As well, the poresize and porosity increase as the added amount increases. The pores areinterconnected with each other and thus become open pores when thecontent of Mg, Zn, and Sn increases.

The inventors of the present invention presume that the reason for thisis as follows. However, the following description is referentiallyprovided for purposes of understanding of the present invention but isnot intended to be a basis for limitation of the scope of the presentinvention.

Mg, Zn, and Sn which are added with Al form a eutectic liquid phase inconjunction with Al at a heat treatment temperature, and Al is partiallymelted. When the liquid phase exists as described above, combination ofthe pores is relatively easily achieved, thus increasing the poresobserved with the naked eye.

Meanwhile, byproduct gases, such as hydrogen, generated through thereaction of molten Al with moisture in the air may be considered thereason for the formation of the pores. It is believed that Mg, Sn, andZn, which have a melting point lower than Al, as well as Al, cause theabove reaction at the heat treatment temperature.

With respect to another reason, it may be presumed that the pores areformed due to a change in density when alloys of metal powders are madethrough partial melting thereof.

The presumption coincides with the fact that relatively many pores areformed by the addition of Zn or Sn in comparison with the addition of Mgas described in the above examples. The reason is that a meltingtemperature (419.46° C.) of Zn or a melting temperature (231.9° C.) ofSn is lower than a melting temperature (650° C.) of Mg.

Taking the above into consideration, in the present invention, the heattreatment temperature must be at least higher than the eutectictemperature of two metals to be mixed with each other. The term“eutectic temperature” as used herein is intended to include aperitectic temperature. However, since the metal powder may contain asmall amount of impurities, partial melting may occur at the eutectictemperature or less. Furthermore, in the present invention, the heattreatment temperature must not be higher than the melting point of pureAl, which has the highest melting point. The reason is that the coatingwill lose structural stability in this case.

EXAMPLE 8

A carbon coating layer was formed on a copper (Cu) plate. After carbonpowder having an average particle size of 5-10 μm was mixed with about15 wt % PVA and dried to produce a carbon cake, it was pulverized in amortar and carbon particles having a particle size of 150 μm or lesswere sorted. The sorted carbon powder was sprayed onto the copper plateat the same temperature and pressure as in the above examples, therebyforming a carbon coating layer.

FIGS. 12 a and 12 b are electron microscope pictures of a section and asurface of the carbon coating layer formed on the copper plate. From thedrawings, it can be seen that the porous carbon coating layer havingexcellent adhesion strength was formed on the copper plate.

INDUSTRIAL APPLICABILITY

A method of the present invention has the existing advantages of a lowtemperature spraying process. In other words, since high temperaturetreatment is not conducted, oxidation of mother material or of a coatinglayer is maximally suppressed, and damage to the mother material due toheat impact does not occur. Furthermore, a very high coating speed canbe assured and it is very easy to control the thickness of the coatinglayer.

Particularly, Mg, Sn, and Zn, which are used in conjunction with Al inthe coating method of the present invention, have a melting point lowerthan Al. Accordingly, since heat treatment is conducted at a meltingpoint of Al or less, the present invention can be applied to mostmembers for thermal and mechanical applications, which include Al or anAl alloy as a mother material, without damage to the mother material.

Furthermore, in the coating method of the present invention, the coatingcomposition is changed to change the porosity of the coating layer.Hence, it is possible to very easily form porous coating layers neededin various industrial fields through the above method.

As well, in a coated member produced according to the method of thepresent invention, it is possible to freely control pore size andporosity. Therefore, it can be used in various members for thermal andmechanical applications.

Additionally, in a carbon coating layer produced according to the methodof the present invention, high thermal conductivity is assured due to aporous structure having many pores, and carbon is much more stable in acorrosive environment, such as sea water or waste water, than metal,thus it is suitable to be used as a member for thermal applications incorrosive environments.

1. A method of forming a porous coating layer on mother material,comprising: providing the mother material; feeding powder having a metalcomposition, which includes at least two different metals selected fromthe group consisting of Al, Mg, Zn, and Sn and which is expressed byxA-(1−x)B (0<x<1, x is a weight ratio of A and B), onto the mothermaterial; supplying high pressure gas to the powder; applying the metalpowder on the mother material by spraying the metal powder using thehigh pressure gas through an supersonic nozzle; and heat-treating thecoated mother material to form the porous coating layer.
 2. The methodas set forth in claim 1, wherein the powder having the metal compositionincludes alloy powder of at least two metals selected from the abovegroup.
 3. The method as set forth in claim 1, wherein A is Al, and Bincludes a metal element selected from the group consisting of Mg, Zn,and Sn.
 4. The method as set forth in claim 1, wherein the supplying ofthe high pressure gas comprises: compressing gas; and pre-heating thecompressed gas.
 5. The method as set forth in claim 1, wherein theheat-treatment of the coated mother material is conducted at atemperature between a eutectic temperature of A and B and a meltingpoint of a metal having the higher melting point of A and B.
 6. Themethod as set forth in claim 1, wherein the heat-treatment of the coatedmother material is conducted at about 200-650° C.
 7. The method as setforth in claim 1, wherein the feeding of the powder further compriseschanging x to change the composition of the powder.
 8. The method as setforth in claim 1, wherein the gas includes any one selected from thegroup consisting of helium, nitrogen, argon, and air.
 9. A metal coatedmember, comprising: metal mother material; and a coating layer formed onthe metal mother material, which includes at least two metal elementsand is expressed by xA-(1−x)B (x is a weight ratio of A and B), wherein,A and B are different metals selected from the group consisting of Al,Mg, Zn, and Sn, x changes when moving in a thickness direction of thecoating layer within a range of 0<x<1, and porosity of the coating layeris changed depending on a change in x.
 10. The metal coated member asset forth in claim 9, wherein x increases or decreases moving in athickness direction of the coating layer, and the porosity of thecoating layer is increased or decreased as x is increased or decreased.11. The metal coated member as set forth in claim 10, where A is Al, Bis any one metal selected from the group consisting of Mg, Zn, and Sn,and x is decreased and the porosity of the coating layer is increasedmoving from an interface of the metal mother material and the coatinglayer to a surface of the coating layer.
 12. A metal coated member,comprising: metal mother material; and a coating layer formed on themetal mother material, which includes at least two metal elements and isexpressed by A-B; wherein, A and B are different metals selected fromthe group consisting of Al, Mg, Zn, and Sn, A or B selected from theabove group changes when moving in a thickness direction of the coatinglayer, and porosity of the coating layer is changed depending on achange in A or B.
 13. The metal coated member as set forth in claim 9,wherein the coating layer includes open pores which are at leastpartially interconnected with each other.
 14. The metal coated member asset forth in claim 13, wherein the open pores exist in an upper part ofthe coating layer.
 15. A method of forming a porous carbon coating layeron mother material, comprising: providing the mother material; feedingcarbon powder which is conglomerated by an organic binder; supplyinghigh pressure gas to the carbon powder; and applying the carbon powderon the mother material by spraying the carbon powder using the highpressure gas through a supersonic nozzle.
 16. The method as set forth inclaim 15, further comprising burning out the organic binder at 400-500°C. after the application of the carbon powder.
 17. The metal coatedmember as set forth in claim 12, wherein the coating layer includes openpores which are at least partially interconnected with each other. 18.The metal coated member as set forth in claim 17, wherein the open poresexist in an upper part of the coating layer.